Longman Dictionary of Contemporary English - underestimate

~1 v 1 to think that something is smaller, cheaper, less important etc than it really is  (People often underestimate the importance of training.) 2 to think that someone is not as good, clever, or skilful, as they really are  (Don't underestimate Manville - he's a skilful campaigner.) ~2 n a guessed amount or number that is too low  (14% may be an underestimate.)